Liquid crystal type displays (LCDs) have recently been studied for use in television systems. Use of liquid crystals in television receivers may be seen in U.S. Pat. No. 4,562,478. This prior device uses back lighting to illuminate a liquid crystal display so that images can be displayed in dark places. The system is small but contemplates black and white TV images although colored back lighting panels are suggested.
The use of liquid crystal configurations for projection television systems has also been considered in the manner shown by Seiko Epson Corp. in ELECTRONICS at page 47 on May 12, 1986. Such prior projection television scheme is illustrated in FIG. 1 of the present application. In this arrangement, light from a tungsten halogen lamp 1 is variously transmitted and reflected through a crossed pair of dichroic mirrors 2 and adjacent mirrors 3 to pass through three liquid crystal displays 4, 5 and 6. These three LCDs modulate three channels to create the red, green, and blue portions of a TV picture. The dichroic mirrors 2 break the white light source 1 into red, blue, and green portions of the spectrum. These three color portions are then recombined by way of a dichroic prism 7. The recombined light is projected by way of a projection lens 8 to a projection screen 9.
In this prior system, the source 1 of light is a tungsten halogen lamp having a small source size which is desirable for high collection efficiency. Since such lamps are deficient in the blue portion of the spectrum, they yield poor color quality.
This arrangement of the prior art in FIG. 1 also includes a condenser arrangement consisting of a condenser lens 10 and reflector 11. The condenser lens 10 is designed for maximum collection efficiency to collect light emitted in the +X direction. The spherical reflector 11 collects light emitted in the -X direction and images the light of the lamp back onto itself.
The difficulty with the prior art systems is that light is lost because the illumination system provides only optimum illumination across the green LCD. Since the red and blue LCDs are farther from the source, they are overfilled with the respective illumination, and light of the respective wavelengths is thus lost. Moreover, owing to its complexity and size, the dichroic prism 7 is expensive.